Tomatoes are extremely high in ascorbic acid, also known as vitamin C. Ascorbic acid is a powerful antioxidant, but it also can make for unpleasantly acidic tomato sauce. Fixing acidic sauce is possible, but it takes a little bit of adjusting and experimenting. The best way to balance an acidic taste is with a sweet one. In the case of sour tomato sauce, a spoonful of sugar makes the acid taste go down.
Bring the tomato sauce to a gentle simmer over medium heat.
Add 1 tbsp. of sugar. Stir the sugar into the sauce with a wooden spoon for one to two minutes or until it is completely dissolved.
Taste the sauce. If it is still too acidic, add another tablespoon of sugar, stir it in and taste the sauce again. It rarely takes more than 2 to 3 tbsp. of sugar to correct acidic sauce.
Wash and peel two to three carrots, depending on how much sauce you have.
Slice the carrots and add them to the sauce. Carrots contain a lot of natural sugar, which counteracts the acid in the tomato sauce as it cooks.
Blend the sauce in a food processor or blender to puree the carrots when the sauce is done, or strain them out with a colander or sieve.
Peel and slice two to three Vidalia onions.
Coat a skillet with olive oil and scatter two to three peeled and sliced Vidalia onions into it.
Toss the onions until they are coated completely with oil. Sprinkle in just enough sugar to barely cover the onions and toss them again.
Turn the heat to medium-high and heat the onions just until the onions start to sizzle.
Lower the heat to warm and cook the onions for 45 minutes to 1 hour, stirring them every 10 minutes or so. Continue with the rest of your sauce recipe once the onions have turned golden brown.